Gastric secretion is produced by epithelial cells in the stomach's gastric glands. These cells include parietal cells, chief cells, mucus-secreting cells, and hormone-producing cells. Parietal cells secrete hydrochloric acid and intrinsic factor. Chief cells secrete pepsinogen, which is converted to the protease pepsin by hydrochloric acid. Mucus-secreting cells produce a bicarbonate-rich mucus that protects the stomach lining. Hormone-producing cells secrete gastrin, somatostatin, and histamine, which help regulate acid secretion.

2. ▪ Gastric secretion is a colorless, watery, acidic,
digestive fluid produced in the stomach .
 Physical properties;
 It is a watery fluid, that has a pale yellow colour , pH is 1-3 ,
the volume secreted per day is 2-3 L .
 The stomach is famous for its secretion of acid, but acid is
only one of four major secretory products of the gastric
epithelium, all of which are important either to the digestive
process or to control of gastric function.
 Chemical composition; It is 97-99% water , it contains
inorganic salts ,and organic components that include ,mucin,
digestive enzymes , hormones

3.  The gastric secretion is produced by the epithelium cells of
the gastric glands .
 Goblet cells or mucus cells:are mucous cells, which
cover the entire luminal surface and extend down into
the glands as "mucous neck cells".
 These cells secrete a bicarbonate-rich mucus that coats
and lubricates the gastric surface, and serves an
important role in protecting the epithelium from
hydrochloric acid and pepsin and other chemical
insults.
.

4. 4
Gastric Mucus-Bicarbonate Barrier

5.  Parietal cells:
 They secrete HCl into the stomach lumen where it
establishes an extremely acidic environment.This
acid is important for activation of pepsinogen and
inactivation of ingested microorganisms such as
bacteria.
 It also secrets the intrinsic factor, a glycoprotein
secreted by parietal cells that is necessary for
intestinal absorption of vitamin B12.

6.  Chief cells:
 It secrets pepsinogen(zymogen). Once secreted,
pepsinogen is activated by stomach acid into the
active protease pepsin, which is largely responsible
for the stomach's ability to initiate digestion of
proteins.
 In children, chief cells also secrete rennin a protease
that helps coagulate milk allowing it to be retained
more longer in the stomach

7. 7
Synthesize and
secrete the HCl acid
responsible for the
acidic pH in the
gastric lumen.
Synthesize and
secrete the protease
precursor known as
pepsinogen.
Produce alkaline
mucus that covers
mucosa layer
Exocrine gland cells of gastric pits

9.  The epithelium cells also produce important
hormones gastrin a peptide that is important in
control of acid secretion and gastric motility and
somatostatin.
G Cells: Gastrin (hormone) ---> HCl secretion
D Cells: Somatostatin (antrum)
Enterochromaffin-like cell: Histamine

10. Gastrin

11.  Makes gastric juice
very acidic.
 Denatures
ingested proteins
(alter tertiary
structure) so
become more
digestible.
 Activates
pepsinogen to
pepsin.
 Pepsin is more
active at pH of 2.0.
Insert fig. 18.9

12. Insert fig. 18.8

13.  Parietal cells secrete H+ into gastric lumen by
primary active transport, through H+/ K+ ATPase
pump.
 Parietal cell’s basolateral membrane takes in Cl-
against its electrochemical gradient, by coupling its
transport with HC03
-.

16. Gastric acid secretion can be divided into three phases:
 Cephalic phase:
 Mediated by the CNS and triggered by smelling, chewing or even the
thought of food
 Mediated by the vagus and accounts for 10-30% of the acid secreted
 Gastric phase:
 Triggered by the presence of food in the stomach (both chemical and
mechanical sensing are involved)
 Accounts for 70-90% of the acid secretion
 Intestinal phase:
 Presence of chyme, most probably amino acids in the intestine
 Triggers approximately 5% of the gastric acid secretion

17. 1. HCl
 converts pepsinogen to pepsin for chemical digestion
 provides optimal pH environment for pepsin
 destroys some bacteria
 stimulates the small intestinal mucosa to release secretin
and CCK
 promotes the absorption of Ca2+ and Fe2+ in small intestine
17

18. 2. Pepsinogen (precursor of pepsin)
 digestion of proteins
3. Mucus
 forms a protective barrier: Mucus-bicarbonate barrier
4. Intrinsic factor
 combines with vitamin B12 to make it absorbable
18

19. Gastric acid secretion is controlled by three mechanisms:
 Neurocrine (by the nerves).
 Endocrine (hormonal-gastrin)
 Paracrine (histamine) in contrast to true endocrines these
hormones are not released into the bloodstream but into the
surrounding tissues and act in the immediate vicinity, e.g.
intestinal mucosal hormones.
19

20.  Stimulated by sight, smell, and taste of food.
 Activation of vagus:
 Stimulates chief cells to secrete pepsinogen.
 Directly stimulates G cells to secrete gastrin.
 Directly stimulates ECL cells to secrete
histamine.
 Stimulates parietal cells to secrete HCl.
 Continues into the 1st 30 min. of a meal.

21.  Arrival of food in stomach stimulates the gastric phase.
 Gastric secretion stimulated by:
 Distension
 Chemical nature of chyme (amino acids and short
polypeptides)
▪ Stimulates G cells to secrete gastrin.
▪ Stimulates chief cells to secrete pepsinogen.
▪ Stimulates ECL cells to secrete histamine.
▪ Histamine stimulates secretin of HCl.

22. G
gastrin
circulation
HCl
vagus
nerve
FOOD
Distension
Peptides
2. Gastric Phase of
Gastric Secretion
(approx 60% of total)
(initiated by gastric events)
G
gastrin
circulation
HCl
vagus
nerve
1. Cephalic Phase of
Gastric Secretion (approx.
30% of total)
(initiated by brain)
B. Functional Phases of Gastric Secretion

23.  Secretion of HCl is also regulated by a negative feedback
effect:
 HCl secretion decreases if pH < 2.5.
 At pH of 1.0, gastrin secretion ceases.
▪ D cells stimulate secretion of somatostatin.

24. 24
Endogenous substances regulating
gastric secretion
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